PSI - Issue 17

Waleed H. Alhazmi et al. / Procedia Structural Integrity 17 (2019) 292–299 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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appears; a crack will extend into the matrix with further increasing load and its path will depend on the strength of the fiber/matrix interface. As mentioned before, there is a marginal contribution of the matrix to the mechanical behaviour of the present unidirectional CFRP. Therefore, the degradation in CFRP is mainly due to the broken fibres. Although there are cracks along the fiber direction in each specimen, bonded end tabs make each specimen as one unite. After the completion of fatigue tests, all specimens were loaded statically to determine their residual tensile strengths. The residual strength normalized by the original strength, based on net stress analysis for both notched and unnotched CFRP plates. The residual strength based on net stress analysis is not dependent on the type of specimen, i.e. notched or unnotched. The residual strength decreases with increasing  f-max /  ult with no effect of d H /w. This may be attributed to fiber-matrix splitting and the broken fibres. Therefore, the residual strength decreases with increasing the broken fibres. This means that, the quality of the fibres, i.e. minimize the flaws in the fibres, is the essential factor in the fatigue strength of CFRP. 5.2. Bolted Joint Tensile Test Fig. 2 shows the effect of e /d H on the SCFs of unidirectional CFRP single-bolt tension joints with  = 0.2, i.e. w/d H = 5. SCFs were calculated based on equivalent, shear, and longitudinal stresses. The calculated SCFs based on equivalent stress are very high due to the high compressive stress ahead of the loaded-bolt. SCFs decrease with increasing e /d H up to e /d H equals three. After that, the effect e /d H is insignificant.

GPa E 11 = 165 E 22 = 11 E 33 = 11 G 12 = 5.3 G 13 = 5.3 G 23 = 3.9  12 = 0.26

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 = 0.2

31

 Eq.  XY  YY Based on

21

11

 13 = 0.5  23 = 0.5

Stress concentration factor

1

0

2

4

6

8

10

e /d H

Fig. (2) Numerical SCFs of Unidirectional CFRP Single-Bolt Tension Joints. The failure mode of all tested bolt-loaded unidirectional CFRP plates is shear-out regardless the values of d H , d B , e , and w or their ratios. This is due to the weakness in the bond between the fiber and matrix or in the shear strength of the matrix compared with the tensile strength of the fiber. Load-bolt displacement responses of all tested bolt-loaded unidirectional CFRP plates are shown in Fig. 3. The static failure is defined as the maximum load, P ult , achieved during the test to failure. As shown in the Fig. 3, the stiffness of the joints is not function of the values of d H , d B , e , and w, whereas, the ultimate load is only dependent on the contact area, i.e. the value of d B . This observation is only acceptable in the case of shear-out failure in unidirectional composite plate, i.e. lower stiffness and strength in transverse direction. (1998)found that the clearance, 1- d H /d B , caused high compressive stress in bearing area, and did not influence the peak tensile stress. On the other hand, Turvey (1998)found that, both the initial stiffness and Pult depend on the w/d H and e /d H for pultruded GRP plate. It is worth to mention that, the reinforcement of pultruded GRP plate is in two forms, viz. E-glass roving (unidirectional fiber bundles) and CFM (Continuous Filament Mat). The CFM provides the transverse stiffness and strength. Further, Turvey found the mode failure changed from bearing to cleavage to shear-out with decreasing e /d H with constant w/d H . However, the mode failure